Transponder location?

[airguy]

I'm getting close to buttoning up the rear top skins on my 9A, and I'm planning on running Dynon glass in the panel along with the Dynon transponder. I'd like to mount the transponder box (about 1 pound) aft of the baggage compartment rather than the avionics bay up front, I'm going to be a bit nose-heavy as it is and I'm moving any equipment aft that I can in order to keep nose-wheel weight reasonable. The battery and strobe power pack will be just aft of the baggage compartment as well.

Soliciting opinions here - any comments/complaints/suggestions with putting the transponder box back there? I have my ADAHRS unit mounted just barely forward of the tail fairing, so the transponder box will be well forward of that, I don't think I'll get any interference with it at least 3 feet away. Any experience or direction from others that have already poked the bear in this area? I'll certainly mount it so that I can just pull the baggage compartment wall and have access to it for maintenance.

[bruceh]

That is what I'm planning on doing. I will be mounting it behind the AP pitch servo bracket, and down under the aft control tube on the rib.

Here is a picture from Jason Beaver's web site that shows where he put the transponder (gold box under the servo).


I'm mounting mine on the other side of that center rib. It will be well back of the AP servo and under the control tube.

[airguy]

I'm thinking I would want mine a little further away from the servo than that, the transponder radio pulse is pretty strong, wouldn't want the servo "twitching" each time it fired from interference.

[Buggsy2]

Originally Posted by airguy

I'm going to be a bit nose-heavy as it is

I'm building a 9A also and this got my interest. How do you know you'll be nose-heavy, and what do you think is the cause?

[airguy]

Originally Posted by Buggsy2

I'm building a 9A also and this got my interest. How do you know you'll be nose-heavy, and what do you think is the cause?

I'm putting an IO-360 up front. That automatically adds 17 pounds forward of the firewall. To counter that I'm going to install the lightweight Whirlwind 200 RV constant-speed prop and move some items aft to try to keep the firewall-forward weight down. ADAHRS, strobe power pack, battery, ELT, transponder, maybe other stuff too - all going behind the baggage compartment.

I want to be able to run 92-octane mogas, which means I'm realistically limited to 8.7:1 compression on the pistons, which means I can't use the stroked IO340 which would give more horsepower on the same weight as the 320 block. If I want both 180hp and Mogas, I have to run the IO360 and accept (and deal with) the forward weight penalty.

[jthocker]

Greg,
Mount it where you proposed. Just did this in a friends RV 8 that way and it works fine. Doing it that way in my RV8 with a Trig. Go for it and build on!

[Camillo]

Greg, I recently finished my RV9A and feel that it is a bit nose heavy (even if CG is within Van's limits). O-320, Hartzell C/S, alternator 60 amp, forward mounted Odyssey battery and a lot of avionics. Of course I placed strobe pack and ELT unit in the tail. This is not enough.

I approve your idea of placing the battery in the tail cone. I have to move mine from the FF to the tail. Van's has an old drawing valid for the RV7 (but it is OK for the 9). I am only guessing where to add the hole which passes through the main longeron assembly: I plan to add a hole just above one of the existing holes at the end of the tunnel and then passing the cable under the front cabin cover (where the fuel and brake tubes pass, too).

[PIN 37]

A forward centre of gravity makes the aircraft more stable, I would have thought that this was not a problem on a 9, different story on a 7 where aeros might be performed??

[Mel]

Forward C/G IS more stable. However too far forward can cause you not to be able to "flare" or "rotate" properly.
This will be even more of a problem if you have the little wheel up front.

[airguy]

Originally Posted by Mel

Forward C/G IS more stable. However too far forward can cause you not to be able to "flare" or "rotate" properly.
This will be even more of a problem if you have the little wheel up front.

Exactly.

I'm not interested in trying to get to a less-stable "neutral" position on the CG - I'm simply moving some items aft that can be moved, to counter the additional weight that I know will be installed up front. If my planning numbers are correct I'll have right at the same amount of noseweight as a standard O-320 with FP prop when it's done, just like Van had in mind. I'm just being cautious about the possibility of becoming the next pogo-stick victim, and trying to keep the nose wheel in the light-duty category (and yes, I already have the Anti-Splat Aero device).